A little more work than for top-level entities, but.... You could use REFEDIT to get into the Xref, identify things there, and REFCLOSE without saving. Or you could use NCOPY and look at what you copied. Or you could do:
(entget (car (nentsel "\nSelect nested object: ")))
for the entity data list of any nested object, though that will usually be a lot more than you want to know, and some of it in inscrutable ways if you're not used to working with entity data lists. And that will always get you the deepest-nested thing [e.g. not a Block in the Xref if that's what you pick on, but a Line or whatever inside that Block]. Unfortunately, LIST won't take (nentsel)'s return as input.
Kent Cooper, AIA